Revive Substrate Crate (#1477)

Closes https://github.com/paritytech/polkadot-sdk/issues/1450

Bringing back the Substrate crate that was forgotten in the monorepo
import 😅

.
It is a doc-only crate. Version number is set to `1.0.0` and publishing
is enabled (so that we can link to docs.rs).

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Signed-off-by: Oliver Tale-Yazdi <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>